Catch Uri.parse() FormatException and skip the URI.

pkg/analyzer/lib/src/dart/analysis/file_state.dart

Index: pkg/analyzer/lib/src/dart/analysis/file_state.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/file_state.dart b/pkg/analyzer/lib/src/dart/analysis/file_state.dart
index facf11f3a5912bfeab5009df057429bfb36ab812..1fdc870638459785ea05120fb8157f05c9144069 100644
--- a/pkg/analyzer/lib/src/dart/analysis/file_state.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/file_state.dart
@@ -492,7 +492,12 @@ class FileState {
    * Return the [FileState] for the given [relativeUri].

[Brian Wilkerson, 2017/01/31 21:51:23]

Maybe mention that `null` is an expected result.

    */
   FileState _fileForRelativeUri(String relativeUri) {
-    Uri absoluteUri = resolveRelativeUri(uri, Uri.parse(relativeUri));
+    Uri absoluteUri;
+    try {
+      absoluteUri = resolveRelativeUri(uri, Uri.parse(relativeUri));
+    } on FormatException catch (e) {
+      return null;
+    }
     return _fsState.getFileForUri(absoluteUri);
   }